Loudspeakers used in compact and portable devices require significant design compromises that may lead to suboptimal sound quality and loudness. A loudspeaker used in a compact device (e.g. a cellular phone, an electronic tablet, a laptop computer, a PDA (personal digital assistant), a media player etc.) is usually small. As a result, the sensitivity of the loudspeaker can be low and the diaphragm on the loudspeaker can have a limited range of motion. Often loudspeakers are overdriven in order to obtain the loudness needed to hear the audio signal coming from it.
Overdriving a loudspeaker can cause a magnet and a voice coil in the loudspeaker to overheat because of the additional current needed to overdrive the speaker. Overheating the magnet in a loudspeaker can cause permanent damage to a loudspeaker. For example, overheating can change the shape of the diaphragm of the loudspeaker. A loudspeaker where the diaphragm has changed shape from its original form distorts sound coming from the loudspeaker.
In addition to changing the shape of the diaphragm, overheating a magnet and a voice coil in a loudspeaker can cause the glue holding the voice coil to the driver to melt. When the glue melts it can cause the voice coil to separate from the driver rending the loudspeaker inoperable. Overheating the magnet and the voice coil can also cause the solder connecting an amplifier to the voice coil to melt, disconnecting the loudspeaker from the amplifier.
Loudspeakers used in compact devices are relatively cheap. However, damage to a loudspeaker in a compact device may cause a return of the entire device. In order to reduce the damage done to loudspeakers and improve the loudness and quality of the loudspeakers, the power applied to a loudspeaker needs to be controlled to reduce overheating of the voice coil in a loudspeaker.